Quiz: The rational method toolbox

1   Overview

We want to refactor the Rational Method toolbox because its current workflow is not efficient when we study multiple watersheds. First, we want to remove the mask parameter to be able to handle multiple watersheds without having to guess the overall extent of the watersheds. Second, we want to combine runoff coefficient computation and flow accumulation processes into one tool called PreprocessTool. The idea is to create non-masked intermediate outputs using the Preprocess tool and use the Rational Method tool to process individual watersheds. Use test_data.zip for testing and validation. Check q2001.txt for final output.

2   Screenshots

3   Penalties

Upload FirstLastname_RationalMethod.pyt to D2L ⇒ Assignments ⇒ Quiz 3 folder.

Debugging: -2 per line added, removed, or edited up to max points per question

Filenames and class names: -2 each

4   Question 1: Remove an unused parameter from the Rational Method tool

10 points

The facc parameter in the Rational Method tool is not used. Remove this parameter from getParameterInfo() and execute().

5   Question 2: Remove the mask-related parameters from the Flow Accumulation tool

10 points

Remove the mask and masked_dem parameters from the Flow Accumulation tool. Remember to remove them from both getParameterInfo() and execute().

6   Question 3: Combine runoff coefficient computation and flow accumulation

30 points

Move runoff coefficient computation from the Rational Method tool to the Flow Accumulation tool and rename the Flow Accumulation tool to the Preprocess tool. Its class name should be PreprocessTool. Remember, we don’t want to apply any mask using the ExtractByMask tool.

7   Question 4: Add a new required input parameter for the runoff coefficient raster to the Rational Method tool

10 points

Since we moved runoff coefficient calculation to the Preprocess tool, the Rational Method tool needs to take a runoff coefficient raster as an input. Add a new required input parameter called runoff_coef for the runoff coefficient raster to getParameterInfo() in the Rational Method tool.

8   Question 5: Apply output watersheds as a mask in the Rational Method tool

20 points

Extract the runoff_coef raster by output watersheds (wsheds_ras) before the cell area calculation where the runoff_coef_ras raster object is first used. Note that the input runoff_coef raster is not clipped to the watershed boundary while the runoff_coef_ras raster is.

9   Question 6: Calculate the total of output watersheds

20 points

Since we use the OBJECTID field in the pencil point layer (outlets), watershed IDs or cell values in the wsheds_ras are greater than 0. Use the following code snippet to add the total area of output watersheds in square miles to the output file.

# grab the raster object
wsheds_arr = arcpy.RasterToNumPyArray(wsheds_ras, nodata_to_value=0)

# count non-zero cells
wsheds_cells = sum(sum(wsheds_arr > 0))

# calculate the total area of watersheds in square miles
wsheds_area = wsheds_cells * YOUR_CODE

Remember that not all DEMs are in the same linear unit. Also, don’t forget to write the following line to the output file:

Area of Watersheds = {wsheds_area} sqmi

10   Bonus question: Reorder and relabel the parameters

10 points

Reorder and relabel the parameters in both tools to have exactly the same interface as the screenshots.